Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The structure of semiconductor material allows the material's electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed operations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each semiconductor die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual semiconductor die from the finished wafer and packaging the die to provide structural support and environmental isolation. The term “semiconductor die” as used herein refers to both the singular and plural form of the words, and accordingly, can refer to both a single semiconductor device and multiple semiconductor devices.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller semiconductor die size can be achieved by improvements in the front-end process resulting in semiconductor die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
A semiconductor die is typically encapsulated and an interconnect structure is formed over the die and encapsulant. FIG. 1a shows semiconductor die 10 covered by encapsulant 12. An insulating layer 14 is formed over semiconductor die 10 and encapsulant 12. A portion of insulating layer 14 is removed by a patterning and etching process, e.g., using photolithography, to form openings or vias 16 and expose contact pads 18 of semiconductor die 10.
In FIG. 1b, a conductive layer or redistribution layer (RDL) 20 is formed over insulating layer 14 and into openings 16 to make electrical connection to contact pads 18. RDL 20 can be formed by a first full surface electroless plated Cu seed layer 20a followed by a dry film resist (DFR) coating which is exposed and developed. A second Cu layer 20b is electrolytic plated within the developed portions of the DFR coating over the Cu seed layer. The DFR coating is then removed, as well as the full surface Cu seed layer outside the RDL pattern. An insulating layer 22, such as solder resist, is formed over insulating layer 14 and RDL 20. A portion of insulating layer 22 is removed by a patterning and etching process to expose RDL 20. Bumps 24 are formed over the exposed RDL 20. Accordingly, interconnect structure 26 formed over semiconductor die 10 and encapsulant 12 includes insulating layer 14, RDL 20, insulating layer 22, and bumps 24.
The formation of interconnect structure 26 involves multiple insulating layers, Cu seed layer, adhesion layer, masking, wet chemical etching, and multiple plating steps. The variety of photolithography processes used to form interconnect structure 26 adds time and expense to the manufacturing process and tends to reduce registration tolerances, alignment compensation, and flexibility in pattern adjustments.